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THE AMERICAN NATURALIST [Vol. XLIX 



The conclusion is open to objection inasmuch as they 

 were comparing a hybrid with a single parental type and 

 in general the greater variability would be expected. 

 Consequently even admitting that lateral conjugation has 

 been a more recent development than scalariform con- 

 jugation, it would not be demonstrated that an error had 

 thus arisen. 



1. Comparative Variability 



Within the limits of the characters studied so far as 

 the present material is concerned, it is evident that the 

 zygospores produced by close breeding are more variable 

 than those produced by cross breeding. While it ds 

 another proposition to extend the conclusion and insist 

 that organisms produced asexually, by pure lines, or by 

 close breeding, are more variable than those produced 

 sexually or by cross breeding, it would seem that the facts 

 strongly support such a conclusion and in connection with 

 the evidence afforded by the investigations of Warren, 

 Ca steel and Phillips, Kellogg, and Wright, Lee and Pear- 

 son, it certainly may be denied that amphimixis or cross 

 breeding as compared with other types actually produces 

 variations, as has long been the prevalent belief. 



The question here of particular interest, however, is 

 that of the excess type of variability represented in 

 Spirogyra. Inasmuch as the material was homogeneous 

 in every way, it may be asserted that the greater vari- 

 ability exhibited by the close-bred forms is not fluctu- 

 ability due to environment. It is also evident that, theo- 

 retically, cross breeding produces a greater number of 

 combinations than inbreeding, nevertheless that the vari- 

 ability thus resulting is overwhelmed by that of another 

 type in nature, is clear from the results noted in the pre- 

 ceding pages. An excellent demonstration of such con- 

 dition is obtained by recalculating constants obtained by 

 Hayes ('12) as shown in the accompanying table (Table 

 IX) based on data obtained in connection with the breed- 

 ing of Nicotiana tabacum. 



